Typically, a wireless communication system makes communications between a fixed base station (BS) and a mobile station (MS) using a single direct link, thus having low flexibility in configuring a wireless network. That is, it is difficult to configure a wireless network to provide services in a wireless environment experiencing fluctuating changes in traffic distribution or the number of required calls.
In this context, studies have been conducted on relaying data over multiple hops using relay stations (RSs) in a wireless communication system. The relay service enables the wireless communication system to reconfigure a network quickly according to a communication environment change and to efficiently operate the entire wireless network. Also, the wireless communication system can provide a high-speed radio channel to an MS by establishing an RS between a BS and the MS. Therefore, the use of RSs provides a high-speed data channel to MSs in poor channel conditions at a cell boundary and expands cell coverage.
The configuration of a conventional wireless communication system for providing a relay service will be described below with reference to FIG. 1.
Referring to FIG. 1, in the relay wireless communication system, MSs 140, 150, 160 and 170 (MS1, MS2, MS3 and MS4, respectively) receive services from a BS 100 and RSs 110, 120, and 130 (RS1, RS2 and RS3, respectively).
MS1 and MS2 within a service area 101 of the BS 100 communicate with the BS 100 using direct BS-MS links L1. MS2, which is in poor channel conditions, receives a high-speed data channel using RS-MS link of RS3, L2.
MS3 and MS4 outside the service area 101 of the BS 100 communicate with the BS 100 using RS-MS links of RS1, L3. That is, the BS 100 can expand its service area by providing communication links to MS3 and MS4 outside the service area 101 using RS1. For MS4 that is at a cell boundary of the service area of RS1 and thus in poor channel conditions, transmission capacity can be increased using an RS-MS link of RS2, L4.
As described above, the wireless communication system can expand cell coverage and increase transmission capacity by providing control channels and high-speed data channels to MSs that are located at a cell boundary and in a shadowing area and thus are in poor channel conditions, by use of RSs. The relay service can be supported using neighbor MSs or separately procured RSs for a relay function.
However, when an MS supports the relay function, the MS consumes its limited power to relay a signal for another MS. The resulting power shortage may impede signal processing in the MS.
Conventionally, there was no sufficient motivation to use an MS capable of operating as an RS in relaying a signal for another MS at the expense of its power consumption in a cellular relay service system designed for expanding cell coverage or increasing transmission capacity, and no related procedures were specified.